Add pseudoinstructions

[Draft]

An implementation is proposed for representing pseudoinstructions in Sail.

The realization is similar to instructions, with a few differences:

1. `union clause ast` -> `union clause pseudo`.

1. `mapping clause assembly` -> `mapping clause pseudo_assembly`.

1. `function clause execute` -> `function clause pseudo_execute`:

   This calls the `execute` clauses for the respective base instructions as
   defined for each pseudoinstruction.

1. `mapping clause encdec`: This is undefined for pseudoinstructions because,
   for one thing, some pseudoinstructions map to more than one instruction.
   This is replaced by a new scattered mapping:
   `function clause pseudo_of`: This maps the pseudoinstruction AST to a list
   of the assembly clauses (strings) of the mapped instructions, for example:

   ```
   function clause pseudo_of(LA(rd, imm)) = [|
     assembly(UTYPE(imm[31..12],rd,RISCV_AUIPC)),
     assembly(ITYPE(imm[11..0],reg_name("x0"),rd,RISCV_ADDI))
   |]

   ```

   This is roughly analogous to `function clause assembly`, but instead
   of representing the instruction syntax, it represents the syntax of the
   mapped instructions.

Makefile

@@ -61,6 +61,8 @@ SAIL_DEFAULT_INST += riscv_insts_vext_fp_vm.sail
 SAIL_DEFAULT_INST += riscv_insts_vext_red.sail
 SAIL_DEFAULT_INST += riscv_insts_vext_fp_red.sail
 
+SAIL_DEFAULT_INST += riscv_pseudos.sail
+
 SAIL_SEQ_INST  = $(SAIL_DEFAULT_INST) riscv_jalr_seq.sail
 SAIL_RMEM_INST = $(SAIL_DEFAULT_INST) riscv_jalr_rmem.sail riscv_insts_rmem.sail
 

model/riscv_pseudos.sail

@@ -0,0 +1,64 @@
+/*=======================================================================================*/
+/*  This Sail RISC-V architecture model, comprising all files and                        */
+/*  directories except where otherwise noted is subject the BSD                          */
+/*  two-clause license in the LICENSE file.                                              */
+/*                                                                                       */
+/*  SPDX-License-Identifier: BSD-2-Clause                                                */
+/*=======================================================================================*/
+
+$ifdef _PSEUDOINSTRUCTIONS
+
+/* ******************************************* */
+/* This file specifies the pseudoinstructions. */
+
+scattered union pseudo
+
+val pseudo_execute : pseudo -> Retired
+scattered function pseudo_execute
+
+val pseudo_assembly : pseudo <-> string
+scattered mapping pseudo_assembly
+
+val pseudo_of : pseudo -> list(string)
+scattered function pseudo_of
+
+/* ******************************************* */
+union clause pseudo = LA : (regidx, bits(32))
+
+mapping clause pseudo_assembly = LA(rd, imm)
+  <-> "la" ^ spc() ^ reg_name(rd) ^sep() ^ hex_bits_32(imm)
+
+function clause pseudo_of(LA(rd, imm)) = [|
+  assembly(UTYPE(imm[31..12],rd,RISCV_AUIPC)),
+  assembly(ITYPE(imm[11..0],reg_name("x0"),rd,RISCV_ADDI))
+|]
+
+function clause pseudo_execute LA(rd, imm) = {
+  if execute(UTYPE(imm[31..12],rd,RISCV_AUIPC)) == RETIRE_SUCCESS &
+     execute(ITYPE(imm[11..0],reg_name("x0"),rd,RISCV_ADDI)) == RETIRE_SUCCESS then
+      RETIRE_SUCCESS
+  else
+      RETIRE_FAIL
+}
+
+/* ******************************************* */
+union clause pseudo = VNEG : (regidx, regidx)
+
+mapping clause pseudo_assembly = VNEG(vs, vd)
+  <-> "vneg.v" ^ spc() ^ vreg_name(vd) ^ sep() ^ vreg_name(vs)
+
+function clause pseudo_of(VNEG(vs, vd)) = [|
+  assembly(VXTYPE(VX_VRSUB, 0b1, vs, reg_name("x0"), vd))
+|]
+
+function clause pseudo_execute VNEG(vs, vd) =
+  execute(VXTYPE(VX_VRSUB, 0b1, vs, 0b00000, vd))
+
+/* ******************************************* */
+
+end pseudo_of
+end pseudo_assembly
+end pseudo_execute
+end pseudo
+
+$endif _PSEUDOINSTRUCTIONS